This invention relates to a melt indexer system wherein the steps required for carrying out the functions of the melt indexing tests are performed by a robot. In the embodiment disclosed in this application, three Goettfert Model MPE melt indexers, substantially modified for robot operation, are utilized. The Model MPE melt indexer is manufactured by Goettfert Werkstoff-Pruefmaschinen GmBH, Buchen/Odenwald, West Germany. A melt indexer is used to determine the relationship of the viscosity of a plastic material, such as a polymer, to its temperature. This information is necessary to control quality and consistency in polymer production essential to the proper uniformity and predictability of downstream characteristics of the polymer. These characteristics include, for example, elongation, reaction to dyestuffs, abrasion resistance to name only a few of many.
Presently, the MPE melt indexer is manipulated manually. Even though test consistency is essential, variations in operator technique substantially effect test results. In addition, the test presently requires close proximity between the operator and high heat. The work is tedious and not well suited to performance by human operators. However, due to the complexity of and the numerous variations in the test, manual operation of the melt indexer has heretofore been required.
In general, the melt indexer operates by heating to a precise temperature a carefully weighed sample of a plastic material in powder or granulated form. When heated, the plastic melts into a viscous mass. The heated mass of plastic is forced by a known weight through a die orifice of a known size. Sensors record data which permits a viscosity index to be determined from a relationship between the viscosity and the temperature of the molten plastic.
Characteristics inherent in the plastic material contribute significantly to the difficulty in achieving consistent test results from human operation of the indexer. The manner in which the indexer is cleaned between each test is particularly important, since any residue from a previous test not only contaminates the sample being tested, but interferes with the proper operation of the machine. Substantial variations in operator technique occur both between different operators and even the same operator from test-to-test and over time. Fatigue, work load and operator morale have all been identified as factors contributing to test inconsistency.